This invention relates to a shell sole for footwear, especially sport shoes, having an edge rising above the inner sole surface, the inside of this edge encompassing the outer edge zone of the shank and being glued or cemented or otherwise connected thereto.
Shell soles of various types and differing structure have heretofore been proposed. They are utilized particularly in sport shoes, since, due to the upwardly rising edge zone of the shell sole, sole material is still brought in contact with the ground even if the shoe rests thereon in an inclined position, and thus an improved grip is obtained. Further advantages of employing shell soles reside in the possibility of a more intimate gluing or other bonding to the shank.
These shell soles, however, also suffer from various disadvantages. Thus, the sole must have a certain strength and/or thickness to prevent small stones and the like from exerting their pressure all the way through the sole to the foot. This results in a relatively hard or thick design of the sole, which renders the latter heavy and relatively resistant to bending. The bending resistance is increased especially by the upwardly rising edge of the shell sole. However, particularly in the case of sport shoes, it is desirable to produce a lightweight shoe which even under considerable dynamic pressure stress will protect the foot from pressure impacts from the sole side, occurring over small areas. Moreover, a sport shoe should be able to follow as closely as possible the motion of the foot, which is of importance especially in the various types of running sports.
Weight and good bending of flexible properties, on the one hand, and the pressure distribution characteristic and firm hold or traction of the shoe even when set on the ground in an inclined position, on the other hand, thus result in the necessity of simultaneously meeting different requirements for the shell sole, notwithstanding the aforementioned conflicting considerations.
It is, therefore, one object of the present invention to provide shell soles of the type described hereinabove evidencing the advantages of a good grip on the floor even when the shoe is in an inclined position and an improved connection or adherence with the shank or upper, without incurring the disadvantages of heretofore proposed shell soles wherein the sole is heavy and resistant to bending and suffers damage, particularly with respect to the bond between the shell and the shank in the edge zone.
The above object as well as other objects and features of the invention are attained by providing several longitudinally distributed predetermined bending, buckling, or flexing zones or points along the edge of the shell sole in the area of the ball of the foot.
In accordance with the present invention, the rigidifying effect of the edge projecting vertically above the sole bottom is reduced in the primary deformation area, namely in the zone of the ball of the foot. Moreover, the appearance of locally restricted bends in the inner and outer ball area, occurring at the same spots, is counteracted by providing a plurality of "predetermined bending points" which are distributed in the longitudinal direction of the sole edge. In other words, the deformation movement which heretofore manifested itself in a correspondingly deep kink always occurring at the same location, is distributed over a greater area. As a result, the mechanical stress on the connection or bond between the edge of the shell sole and the shank is distributed over a larger area, whereby the specific loads or stresses thereon are reduced and a longer lifetime is obtained for this bond. Moreover, the pressure stress acting on the foot due to the bend or kink formation is correspondingly distributed as well.
In one of the preferred embodiments, the predetermined bending points or zones are established or formed by relatively thin wall portions of the material remaining between webbed portions or sections or stress alleviating inserts provided according to the invention along the upwardly rising edge zone of the shell sole formed so that they terminate approximately perpendicularly to the plane of the sole. The webs thus impart strength to the sole in the edge zone, whereas the thin-walled portions of material remaining therebetween are deformed under the bending motion and/or can also be buckled in the direction toward the shank, depending on the material and the bond. Since the shank materials are generally comprised of a material which lends itself to a buckling to a lesser extent than the shell sole, such as leather, textile materials, and correspondingly soft plastics, the bond between the inside of the shell sole edge and the shank is exposed only to minor stresses during the rolling motion of the foot. The connecting layer, for example, an adhesive or the material of the shell sole proper, is likewise capable of bending or buckling.
In another preferred embodiment of the invention, the webs are formed to taper in the upward direction; tapering may be with respect to the thickness of the webs approximately vertically to the shank surface and/or also in the longitudinal direction of the edge with respect to the width of the webs. In the latter case there remain between the webs approximately triangular shaped zones of reduced thickness of material.
As emphasized above, the greatest bending stresses occur during the rolling motion of the foot in the zone of the ball thereof. However, also toward the zone of the toe and toward the heel zone the sole is correspondingly deformed, so that in certain embodiments, these predetermined bending points or buckling zones may extend fron the end of the toe region to the beginning of the heel region and preferably in the inner as well as outer ball zones.
A further embodiment of the shell sole directed to solving the aforementioned problem resides in forming a cutout or recess in the area of the shoe bottom of the shell sole. Depending on the purpose of the shoe associated with the shell sole, shoe bottom parts of various material characteristics can be inserted in this cutout. This affords the possibility of producing the shell sole proper of a relatively rugged and/or bending-resistant material, so that a good pressure distribution is ensured even with a thin sole design with regard to ground unevennesses, such as stones and the like. In contrast thereto, the insert sole bottom or bottom inserts may be made of a relatively soft and/or also lightweight material offering only a minor resistance to the bending or twisting of the sole during the rolling motion of the foot. With the insert, the sole in total has, in spite of the relatively firm material for the outer sole, only a minimal bending resistance, especially in conjunction with the above-described constructions of the edge zone of the shell sole.
The possibility of inserting, in the cutout of the sole bottom, insert sole bottoms of different material and properties which can be, depending on the ultimate intended purpose of use for the shoe, more or less soft, perspiration-absorbing, lightweight, elastic, shock-absorbing, and the like, furthermore has the special advantage that the same mold can be used for manufacturing shell soles having, due to the utilization of differing materials, correspondingly different characteristics. Therefore, with only a single shell mold, quite a large array of requirements can be met for sport shoes intended for a great variety of types of sports. This is of special economical significance, considering that the mold for such shell soles is relatively quite expensive.
The cutout when present need not extend over the entire bottom of the shoe and it is possible to provide individual recesses in the ball and/or heel zones. It is likewise possible to subdivide the insert sole bottoms, i.e., to insert materials with different characteristics in different regions of the sole. In a preferred embodiment, the cutout extends over the entire bottom of the shoe, except for a marginal zone which preferably is of approximately the same width all around. Basically different inserts extending over certain regions of the cutout can be introduced into such a cutout. In view of the stresses, which occur, and also economical considerations, however, it will usually be desirable to make do with a single material for the insert. For similar reasons, in another preferred embodiment, the cutout is of approximately the same depth over its entire expansion as seen when viewed perpendicularly to the bottom of the shoe. Such a construction is not absolutely required and, therefore, it is possible, especially when subdividing the cutout into different zones, to provide differing depths. Also, the heel portion of the shell sole, which is normally fashioned to be thicker, will be rendered lightweight by providing a honeycomb-like structure, for example, from the wear zone of the thread sole upwards to the underside of the insert. Also with a view toward a reduction in weight and, additionally, a further reduction in weight and, additionally, a further reduction in bending resistance, it is possible to arrange recesses in the marginal zone of the shoe bottom encompassing the cutout, which recesses are likewise extended preferably to the wear zone of the tread sole. These recesses can have varying configurations; for example, they can be vertically extending holes with defined edges, or also zig-zag-shaped recesses, and the like.
Another preferred embodiment resides in that the edges of the cutout are made to be undercut, at least in certain regions. Thus, an insert sole bottom can then be readily placed into the correct position and can be sufficiently fixed in position for use without any further fastening means due to this wedge-shaped and/or half-dovetail-like holding arrangement.
The webbed portions or stress alleviating inserts of the invention which provide the shell sole with longitudinally distributed predetermined bending or flex points may be derived from the same or different material as the shell sole and/or shank including natural, or artificial leather, flexible plastics, textiles, rubber and the like. Moreover, the web portions may be molded or otherwise formed integrally with the edge zone of the shell sole or may be formed separately as an insert or underlay prior to completion of the edge zone.
Other objects, features and advantages of the invention will be apparent to those skilled in the art by reference to the attached drawings and detailed description of the invention which follows.